1. Field of the Invention
The present invention is in the field of control systems, and more specifically, is in the field of very low speed vehicle control algorithms.
2. Discussion of the Prior Art
In the prior art, performance of the existing control system deteriorates at very low speeds. A very low speed operation is considered to be in the range of (0.0-1.0) mph, or (0.0-0.5) m/s, and is necessary for certain farming operations.
Performance of the existing system deteriorates at low speeds for several reasons. At first, the sensor data is limited. At speeds less than 0.5 mph RTK GPS velocity and heading become noisy and unreliable; the signal to noise ratio of yaw rate from the Inertial Measurement Unit (IMU) deteriorates, and finally at speeds less than 1 mph, the vehicle speed sensor (VSS) no longer provides useful information. A reliable estimate of vehicle speed is necessary in the existing controller because of the dual mode operation of the heading filter (clamped versus normal mode); the activation or deactivation of the steering loop, and speed related dependencies in the outer supervisor loop. Also, at very low speeds, the vehicle has a large time constant that leads to problems of integrator windup and saturation in the supervisor loop.
What is needed is to enhance the existing navigation control algorithms such that closed loop performance at low speeds is comparable to what is currently achievable at higher speeds (approx. 0.5 m/s-1 m/s).